In an absorption chiller or an absorption chiller/heater, the concentration of a liquid solution varies during circulation thereof in a vacuum vessel, and the variation of concentration generates chilled water or hot water to be introduced in to heat exchangers installed in rooms air-conditioned. The solution contains an absorbent, e.g., lithium bromide, lithium chloride, lithium iodide or the mixture thereof.
A single effect absorption machine has an evaporator, an absorber, a generator and a condenser in a vacuum vessel. As shown in FIG. 1 a double effect absorption machine has a high temperature generator 5 in another vacuum vessel besides above mentioned evaporator 1, absorber 2, low temperature generator 3 and condenser 4 in a main vessel.
An evaporator tube 1A is disposed in the evaporator 1. Refrigerant 24 in a refrigerant reservoir 1B is pressurized by a refrigerant pump 14 and is sprayed over the surface of evaporator tube 1A. As internal pressure in the vacuum vessel is extremely low, refrigerant 24 on the outer surface of evaporator tube 1A is evaporated by the heat of water 21 which passes through evaporator tube 1A. On the other hand the heat of vaporization of refrigerant 24 cools the water 21 in evaporator tube 1A. The water 21, i.e., chilled water 21a is introduced into heat exchangers (not illustrated) installed in rooms air-conditioned. The chilled water 21a is heat-exchaged with air in rooms by the heat exchangers. The chilled water 21b heat-exchanged is returned to the evaporator tube 1A by a chilled water pump 13. A pipe for introducing chilled water 21a into heat exchangers is provided with a temperature sensor 8 in order to detect an outlet temperature of the chilled water 21a.
An absorber 2 has an absorber tube 2A therein. The refrigerant vapor 20b generated in an evaporator 1 flows into the absorber 2. When sprayed solution 23a absorbs refrigerant vapor 20b, absorption heat is generated in the absorber 2. Since the absorption heat increases a temperature of concentrated solution 23a, the capacity which concentrated solution 23a absorbs refrigerant vapor 20b decreases. In order not to decrease the capability of absorbing refrigerant vapor 20b, cooling water 22 is fed to the absorber tube 2A. As the concentrated solution 23a is cooled, the solution recovers its capability to absorb refrigerant vapor 20b. The concentrated solution 23a absorbs much refrigerant vapor 20 so that a pressure in a vacuum vessel is kept at high vacuum. This absorber 2 is provided with a solution pump 15 to supply solution 23 in a solution reservoir 2B to low temperature generator 3.
A low temperature generator 3 is provided with a generator tube 3A into which refrigerant vapor 20a separated in a vapor separator 20 downstream a high temperature generator 5 is introduced. The dilute solution 23 supplied to the low temperature generator 3 by a solution pump 15 is heated by refrigerant vapor 20a. The refrigerant vapor 20c evaporated from dilute solution 23 in a low temperature generator 3 flows in to a condenser 4.
A high temperature generator 5 is provided with a heating device 9 by which solution 23b in a high temperature generator 5 is heated. The solution 23b heated under high vacuum is concentrated so that water vapor is generated from solution 23b as refrigerant vapor 20a.
A condenser 4 has a condenser tube 4A therein into which cooling water 22 after passing through an absorber tube 2A is introduced continuously. The refrigerant vapor 20a flowed from generator tube 3A and refrigerant vapor 20c evaporated in a low temperature generator 3 are cooled by a cooling water 22 which flows in a condenser tube 4A. The refrigerant vapor 20a and 20c are condensed into refrigerant 24.
Passage of cooling water 22 from an absorber tube 2A to a condenser tube 4A rises a temperature of cooling water 22, which is discharged from a condenser tube 4A so that it i cooled by a cooling tower (not illustrated) and is returned to the absorber tube 2A by a cooling water pump 12.
The absorption chiller/heater can perform not only above mentioned cooling operation but heating operation. Under cooling operation a cooling/heating switch valve 28 is closed. On the other hand under heating operation the switch valve 28 is opened.
Under both cooling operation and heating operation high temperature refrigerant vapor 20a from a vapor separator 20 is introduced into a low temperature generator 3. Alternatively, high temperature steam is introduced into a low temperature genera for 3 from a separately provided steam generator (not illustrared). High temperature refrigerant vapor 20a or high temperature steam heats dilute solution 23 in a low temperature generator 3. In the high temperature generator 5, fuel gas, e.g., town gas, LPG gas and natural gas or oil is burnt by a heating device 9. Alternatively, high temperature steam is introduced into a high temperature generator 5 from a separately provided steam generator. By combustion of fuel gas or oil or by the heat of high temperature steam the solution 23b in a high temperature generator 5 is heated.
The cooling capability of an absorption chiller or an absorption chiller/heater depends on a temperature of the chilled water 21b returned to an evaporator tube 1A or on a temperature of the chilled water 21a flowed out evaporator tube 1A and on a temperature of the cooling water 22 which is fed from absorber tube 2A to condenser tube 4A. For example, notwithstanding the fact that a temperature of the cooling water 22 is slow, when a temperature of the chilled water 21a detected by a temperature sensor 8 is higher than that of controlling target, a heating quantity of the high temperature generator 5 is adjusted by subjecting to a proportional control or a PID (proportional, integral and differential) control which is based on an outlet temperature of the chilled water 21a, so that an opening degree of the burning quantity control valve 10 is increased, and solution 23b in a high temperature generator 5 is heated up. A large quantity of refrigerant vapor 20a is generated from solution 23b, which is concentrated more.
As described above, when a temperature of cooling water 22 is low, dilute solution 23 in the solution reservoir 2B of absorber 2 falls in temperature. As concentrated solution 23a which is introduced into the low temperature heat exchanger 6 through a high temperature heat exchanger 7 from the vapor separator 20 is cooled by the dilute solution 23 supplied to the low temperature heat exchanger 6 by a solution pump 15. According to strongly cooling the solution the absorbent crystallizes from the concentrated solution 23a. When the crystallized absorbent is deposited on the outlet 6a of a low temperature heat exchanger 6, choking at the outlet 6a thereof occurs. As a result, the absorption chiller or the absorption chiller/heater becomes inoperable.
In order to maintain a normal operation of an absorption chiller or an absorption chiller/heater, the following methods are adopted.
One method is to limit a heating quantity in the heating device 9 so that it is not more than a maximum heating quantity determined based on a temperature of the cooling water 22. Thereby the concentrated solution 23a introduced into the low temperature heat exchanger 6 is prevented from being excessively concentrated.
To state for reference, a single effect absorption machine is provided with neither high temperature generator 5 nor high temperature heat exchanger 7. In case of applying the above mentioned method of limiting a heating quantity to the single effect absorption machine, the amount of the steam supplied to a generator tube 3A from as team generator is limited.
However, cooling operation of an absorption chiller or an absorption chiller/heater depends on not only a temperature of the cooling water 22 but a temperature of the water 21 in the evaporator tube 1A, a temperature of the concentrated solution 23a and a heating quantity of the heating device 9. If the above mentioned method is adopted, the heating quantity which is suitable for any operating condition may not often be obtained, and the concentration of concentrated solution 23a becomes insufficient to any desired operation.
Another method is to return the amount of refrigerant 24 determined according to a temperature of the dilute solution 23 in an absorber 2 from a condenser 4 to the refrigerant reservoir 1B of an evaporator 1, to the solution reservoir 2B of the absorber 2 or to a low temperature heat exchanger 6 through an unshown solenoid valve.
Returning refrigerant 24 to the refrigerant reservoir 1B or to the solution reservoir 2B may reduce concentration of the circulating solution in whole. The concentration of the concentrated solution 23a in a low temperature heat exchager 6 can be also reduced by returning refrigerant 24 to the low temperature heat exchanger 6. In both cases over-concentrating solution and crystallizing absorbent are able to supressed, however, the heating quantity which is used to generate returned refrigerant 24 is wasted.
It is thus an object of the present invention to provide a heating quantity suitable for an allowable operating condition of an absorption chiller or an absorption chiller/heater even when conditions of the cooling operation thereof vary, thereby making it possible that the concentration of solution introduced into a heat exchanger is controlled so as to match with any cooling operation, and preventing a part of heating quantity consumed for generating refrigerant from being wasted.